This invention relates to dredges, and, more particularly, to grizzlies for such a dredge which separate recoverable material from material to be discharged or waste material.
Water-based and floating dredges typically include one or more bucket or clamshell-types grabs which are lowered into a waterway to collect sand, clay, gravel or the like from the bottom of the waterway. The grab typically deposits the collected material onto a grizzly which often includes a sieve having a plurality of generally parallel bars. The dredged material often contains components whose value justifies recovering them such as sand and gravel. Other components, such as clay, are not desirable for recovery and are simply collected for removal and disposal. Separating the recoverable material from the material to be discharged, however, in the past has been an inefficient and often time consuming process. Frequently, the dredged material includes a wide variety of materials. In other words, rarely does the dredged material include entirely recoverable material or entirely waste material to be discarded.
The time and expense involved in recovering useful material through a water-based dredging operation are very significant. Therefore, it is important to effectively and efficiently retain all of the available recoverable material from a given load. Currently, one common method for dredging is to deposit or dump the load of dredged material in the grab onto a primary grizzly for further processing. Once the dredged material is deposited onto the grizzly, smaller materials, such as sand and gravel, pass through the bars of the grizzly for recovery and further processing. The material remaining atop the grizzly is then discharged therefrom.
One manner of discharging the material remaining atop the grizzly is disclosed in U.S. Pat. No. 5,588,536 issued to the present inventor and hereby incorporated by reference in its entirety. In that patent, the dredge includes a bi-directional grizzly which includes a rake structure that can be operated in either of two opposite directions. If the material remaining atop the grizzly includes sufficient recoverable material for further processing, the rake is operated in a first direction to discharge that material directly into in a crusher or the like. However, if the material remaining atop the grizzly is not worthy of recovery, the rake is operated in a second opposite direction for discharge of the material down an inclined chute and onto a refuse barge, conveyor or the like.
However, the material remaining atop the primary grizzly often includes a mixed variety of components. For example, the remaining material may include larger rocks, gravel or the like which are too large to pass between the spaced bars of the primary grizzly but are still worthy of recovery for further processing. Nevertheless, the material remaining atop the primary grizzle often includes clay and/or other waste along with the recoverable components. The operator of the dredge then must decide whether to discard the entire contents of the material atop the primary grizzly or further process the waste material included therein in an effort to retain the available recoverable material. This dilemma often results in the discharge of a significant quantity of worthwhile recoverable material or processing of clay and other undesirable elements resulting in an inefficient and ineffective dredging operation.